1. Field of the Invention
The present invention generally relates to a light-emitting diode (LED) device, and more particularly to an LED device with a conductive defect layer.
2. Description of Related Art
One common technique of increasing luminescence efficiency of a light-emitting diode (LED) is to use a tunnel junction to stack two or more LEDs. The stacked LEDs emit more light and are brighter than a single LED. The tunnel junction also enhances current spreading, which allows more carriers to perform recombination. Further, the stacked LEDs have fewer electrodes than individual LEDs yielding the same amount of light, therefore saving space and reducing electromigration associated with the electrodes.
One conventional method of forming the tunnel junction is to employ a heavy doping technique, for example, as disclosed in U.S. Pat. No. 6,822,991 entitled “Light Emitting Devices Including Tunnel Junctions.” As a tunnel distance of the tunnel junction is usually small, it is ordinarily difficult to obtain an expected tunnel junction by the heavy doping technique. Moreover, heavy doping may disadvantageously affect the doping concentration of a neighboring layer.
Another conventional method of forming the tunnel junction is to employ a polarization technique, for example, as disclosed in U.S. Pat. No. 6,878,975 entitled “Polarization Field Enhanced Tunnel Structures.” The polarization technique, however, requires complex process control and unduly limits fabrication material selection.
Another common technique of increasing luminescence efficiency of the LED is by forming an ohmic contact on an electrode. One conventional method of forming the ohmic contact employs the heavy doping technique. The heavy doping, nevertheless, may disadvantageously affect the doping concentration of a neighboring layer.
A need has thus arisen for a novel LED structure to alleviate the problems mentioned above.